Regulation of chromatin structure plays a major role in all studied processes in the nucleus. The primary building block of chromatin is the nucleosome. This particle contains two copies each of four core histones; these proteins which form a core which organizes 146 base pairs of DNA. The nucleosome, once thought of as a static building block, is now known to be dynamic. A large class of complexes, the ATP-dependent chromatin remodeling complexes, use the energy of ATP hydrolysis to remodel nucleosome structure and position. A major focus of this application is to explore the extent to which remodeling complexes differ in function. A mechanistic understanding of the full spectrum of activities of this family of complexes is necessary to understanding the ways in which chromatin structure can be modulated, and how modulation of chromatin structure might contribute to the regulation of nuclear processes. This will be done by comparing SWI/SNF-family remodeling complexes with other remodeling complexes in three Aims: Aim 1: The role of the ATPase domain in remodeling. We will create chimeric proteins with 'swapped' ATPase domains to define the role of the ATPase domain in function. Aim 2: Characterization of the effects of histone variants on the remodeling reaction. We will test the ability of several different remodeling proteins to function on nucleosomes that have been assembled with different histone variants. Aim 3: ATP-dependent remodeling and higher order chromatin structure. We will use quantifiable approaches to examine the effects of changes in linker length and compaction status on remodeling by a spectrum of remodeling proteins. We will develop a tissue culture system to characterize the magnitude and spread of changes in chromatin structure caused by different remodeling activities. [unreadable] [unreadable]